Rare H5N1 viruses can mutate easily; spillover to humans more likely

 

In a study published in Nature Communications, an international team of researchers shows how evolution can favor mutations that make avian flu more transmissible in mammals.

The team led by Thomas Friedrich, a professor of pathobiological sciences at the University of Wisconsin-Madison School of Veterinary Medicine, found that during transmission, when one animal is infected by another through sneezing or coughing, the process of natural selection acts strongly on hemagglutinin, the structure the virus uses to attach to and infect host cells.

Perhaps their most surprising and troubling discovery was that mutations present in only about 6 percent of the viruses infecting one ferret could be transmitted to another. This suggests that even very rare mutants can be transmitted if they have an evolutionary advantage.

The data, Friedrich says, indicate that viruses capable of infecting humans probably already exist in nature, but at very low frequencies. Those findings, he adds, suggest that current surveillance methods may be missing H5N1 viruses capable of making the leap from birds to humans.

The new work drew on transmission studies conducted last year in the lab of Yoshihiro Kawaoka, a co-author of the new study and also a professor of pathobiological sciences at the UW-Madison School of Veterinary Medicine.

“Fully avian viruses may act differently in nature,” he notes. “But the data suggest to us that it wouldn’t take many viruses from a chicken to infect a person, if the right mutations were there — even if they were a tiny minority of the overall virus population. I suspect that result will hold true.”

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